And more importantly - will they be looking? We are only looking at small portion of the sky at a time. At the same time in order to send messages to other star

And more importantly - will they be looking? We are only looking at small portion of the sky at a time. At the same time in order to send messages to other stars powerful telescopes need to be utilized. You can't simply build a telescope per star with a planet that is thought to contain life and broadcast all the time. Thus, if civilization is not capable to monitor all of the sky at the same time with low powered telescopes and quickly point high powered telescopes when something interesting is detected, there is extremely small chance that it would be able to communicate effectively. That is retransmitting the signal to the same star is worth inherently less when compared to trying to transmit to a new star. If interstellar travel is not viable, what we would want to do is transmit wikipedia[0] to all stars that could contain life. Traveling time for information would be long enough that we can't expect confirmation or two way communication. So what you would want to do is make a really powerful telescope beaming wikipedia to one star at a time (or many telescopes transmitting to different stars). Idea is - you do not want to repeat yourself. If you sent information once, and it have not been received, you would not want to try again for a long while. That is due to the fact that chance that civilization would develop that can listen to your signals in relatively short amount of time is unlikely. So I would say that if this is logic transmitting civilization would use then a signal would not be repeated for thousands of years. While writing this I though of algorithm that might work better to maximize amount of civilizations you reach. This would require a relatively stable space transmitter, or series of coordinated ground transmitters: 1. Pick a set of stars S that potentially can support advanced civilization and are located closely in a region of space (so you do not have to reposition telescope a lot). 2. Start sending signals primer signals to stars. For signal S[x], temporal difference between S[x] and S[x+1] would a set amount shorter than temporal distance between S[x-1] and S[x]. Primer signals are short and cheap, transmitting entire Wikipedia should take way longer (Weeks, months, maybe years?). 3. Once time between primer signals reaches some threshold start transmitting data set. Idea is that this will give advanced civilization potentially listening a chance to prepare to receive full transmission, while avoiding costly repeats of big data set. [0] Wikipedia is chosen as sufficiently large volume of knowledge about human civilization that we would potentially want to transmit.